A conventional ink cartridge for an inkjet printer is formed with an ink outflow port and an air inflow port. Ink stored in an ink tank is supplied to a recording head via the ink outflow port. Internal space of the ink tank is in communication with atmosphere via the air inflow port. With this structure, pressure difference between interior and exterior of the ink tank is substantially eliminated by introducing air into the ink tank for an amount corresponding to an amount of ink supplied to the recording head.
Japanese Utility Model Publication No. HEI-5-35284 discloses a structure for detachably mounting the above-described ink cartridge on a holder from which a pair of hollow needles projects upward. The hollow needles penetrate into a rubber plug provided at the bottom of the ink tank when the ink cartridge is mounted on such a holder. One of the hollow needles is used as the ink outflow port and the other as the air inflow port.
However, ink stored in the ink tank may leak out through the air inflow port as the latter is in communication with atmosphere. In order to prevent the leakage of the ink, an air intake tube is vertically provided internally of the ink tank so that the lower end of the air intake tube is connected to the air inflow port and the upper opening of the air intake tube is positioned above the surface of the ink in the ink tank. Further, a hydrophobic filter is attached to the upper opening of the air intake tube to block ink flow thereinto.
When troubled inkjet printers are sent to the service center for repair or defective inkjet printers are sent back to the manufacturer, the inkjet printers with the ink cartridge need to be transported. During transportation, it is impossible to hold the printers in a normal use orientation, so the ink cartridge slanted from the vertically oriented normal position causes the top opening of the air intake tube to immerse into the ink. In such a case, the hydrophobic filter attached to the top opening of the air intake tube prevents the ink from leaking out with the ink cartridge disclosed in Japanese Utility Model Publication No. HEI-5-35284.
However, during transportation which may be land transportation, water transportation, or air cargo transportation, temperature and atmospheric pressure in the environment of the cargo may abruptly change. When the pressure in the ink tank increases with the top opening of the air intake tube immersed in the ink, ink can ooze out from the hydrophobic filter. The ink thus leaked out from the air intake port stains the inkjet printer.
Japanese Patent Application Publication No. HEI-8-90783 also discloses an ink tank for an inkjet printer. In the inkjet printer disclosed therein, pressure change in the interior of the ink tank does not cause ink to leak out through an air inflow port. To attain the goal, an ink absorbing member is disposed within the ink tank and a rib is formed in the portion close to the air inflow port in order to prevent the ink absorbing member from directly contacting the air inflow port.
However, the ink tank provided with the ink absorbing member and the rib increases the cost of ink cartridge.